Measurements of heart and pulmonary pressures are very significant for diagnosis of systolic and diastolic heart failures, ventricular infarction, and other heart conditions. Specifically, such pressures are directly related to the mechanical properties of the cardiac muscle and, as such, different parameters of the cardiac cycle can be used to determine the status of a patient's heart function and/or to diagnose specific heart-related conditions.
Conventional monitoring and measuring techniques are typically invasive, often requiring sensors or other measurement devices to be placed within the heart or the vessels connected thereto. Such invasive measurements are costly, time-consuming and potentially dangerous to the patient. For example, conventional methods dictate catheterizing the left ventricle of the heart to obtain a direct measurement of left ventricular end-diastolic pressure (LVEDP). However, catheterizing the left ventricle is both highly invasive and risky, as it is associated with serious complications including stroke and death. Accordingly, the conventional invasive techniques used to obtain direct pressure measurements from a heart are undesirable as routine diagnostic tests and are impractical in a non-clinical setting.
While some techniques exist for non-invasively measuring heart and pulmonary pressures during the cardiac cycle, such techniques are limited and, in some cases, only approximate the desired measurements. For example, in the absence of aortic valve disease, left ventricle (LV) systolic pressure (PLVSP) equals the synchronous aortic pressure (i.e., PLVSP=PAP) and can therefore be accurately determined noninvasively. However, the non-invasive estimation of LVEDP, right ventricle (RV) pressure, and pulmonary pressure is currently a great challenge using conventional techniques. The LVEDP is empirically estimated from pulmonary venous and mitral flows, which lacks a theoretical basis and, at best, provides only an approximation of the targeted pressure. Furthermore, the non-invasive method for assessing RV and pulmonary pressures is to add the transtricuspid pressure gradient (computed by a modified Bernoulli equation based on the maximum velocity of the regurgitant jet) to the mean right atrial pressure (estimated clinically from the jugular veins). It is difficult, however, to non-invasively measure jugular vein pressure and to accurately compute the transtricuspid pressure gradient using a modified Bernoulli equation in patients. Hence, there exists a clear clinical need for improved methods for the non-invasive determination of LVEDP, RV and pulmonary pressures, based on laws of mechanics and not simply empirical data.